The increasing level of sophistication in both computer software and computer hardware has found particular application in the test and measurements field. In particular, computer simulation enables the evaluation of devices and processes in a simulated real-time mode. There are numerous advantages to such active mode test devices. First, once the computer hardware is established and the software developed, it is possible to test equipment and processes under a wide variety of real-time conditions. This leads to a very cost effective testing system because it makes unnecessary the need to duplicate environmental conditions to test hardware malfunctions.
The use of computer simulation also significantly decreases the amount of time necessary to conduct tests of devices and processes. Since it is common to assemble a computer simulation chamber within the laboratory, tests can be run much more quickly than if there was a need to conduct the tests under actual environmental conditions.
Also, computer simulation facilitates frequent testing and permits a design to be repeatedly tested and modified before assembling a working prototype of the device for actual test purposes. This can significantly shorten design and development times.
Computer simulation has found important application in the development and testing of missile seekers. It is far easier and more efficient to test in a laboratory the response of a new seeker design to various simulated conditions instead of having to acquire a test site and evaluate the seeker under actual flight conditions.
In the past, two types of missile seekers have evolved. They are the passive, e.g., infrared and optical, and active such as radar or microwave.
Passive millimeter wave seekers derive their target and guidance data from contrast differences between a target and its surrounding background due to variations in thermodynamic temperature (emissivity relationship) and reflectivity (sky temperature). This can be expressed by the following equation: EQU T.sub.R =eT.sub.T +pT.sub.SKY
where
T.sub.R =The radiometric temperature (K) of the target or background at the frequency of the millimeter wave seeker. PA1 e=The emissivity of the target or surrounding background terrain at the seeker's operating frequency. PA1 T.sub.T =The thermodynamic temperature of the target and surrounding terrain (K). PA1 p=The reflectivity of the target and the background at the seeker frequency. PA1 T.sub.SKY =The sky temperature (K) at the seeker frequency.
Active millimeter wave seekers use radar techniques for their guidance, i.e., transmit a specific waveform and frequency and home on the energy reflected from the target and the surrounding background.
Each of the active and passive missile seekers has its advantages. For instance, active seekers provide very good target resolution at long distances. At close range, however, radar and other types of active seekers suffer a well-known problem in the art called glint.
Passive seekers also have long range application but, perhaps more importantly, do not exhibit glint at close range. Accordingly, it has become desirable in some applications to provide a dual mode missile seeker which incorporates both passive and active seekers on the same missile.
Such dual mode seekers, however, have given rise to a host of questions resolvable only through testing and design optimization of the seekers. These questions include the likelihood of interference between the active and passive missile seekers, the compatability of different designs of active and passive seekers, and the optimal way of interfacing the two seekers.
It has been known to employ anechoic radar simulators to provide real-time simulations for active missile seekers. Anechoic radar simulators cannot, however, provide passive millimeter wave real-time simulation because of the high emissivity characteristics of the anechoic material and the resulting high thermodynamic temperatures which mask the passive seeker under evaluation. Accordingly, a passive/active (dual mode) millimeter wave seeker cannot be evaluated in an anechoic chamber.
A simulation facility for dynamically testing guidance systems which use radio frequencies is disclosed in U.S. Pat. No. 4,106,345 issued to Saunders et al. on Aug. 15, 1978. This patent is assigned to the assignee of the instant invention.
The Saunders et al. simulation facility enables the testing of passive seekers in the radiometric frequency band comprising generally the millimeter and microwave frequency ranges covering from 18 GHz to 350 GHz. The simulator facility includes a chamber having interior walls lined with a reflective material having a very low emissivity coefficient, such as aluminum foil. A portion of the ceiling of the chamber is open to the sky and a 45.degree. sloping surface is provided beneath the ceiling opening. An array of dynamically controlled noise sources is arranged within the chamber, and, when energized, emit energy at radiometric frequencies to simulate the radiometric appearance of terrain and selected objects and targets. A passive seeker is provided in the sloping surface such that radiometric energy emitted by the array not captured by the passive seeker is reflected off of the sloping surface and through the ceiling opening to the sky.
An attempt to employ this facility to support dual mode seeker simulation when anechoic material was placed in the aluminum foil lined chamber failed because the ambient radiometric temperature (energy) of the chamber was increased to an unworkable level.